1. Field of the Invention
The present invention relates to an apparatus for transforming a three-color signals into a multi-color signal to display an image, and more particularly, a method and apparatus for transforming a three-color signal into a multi-color signal, by which multiple color signal values corresponding to reference variables extracted from an input color signal composed of three color components are determined from a lookup table, and the found multiple color signal values are used to extract the remaining multiple color signal values.
2. Description of Related Art
With a development of electronics engineering, information provided to users includes not only simple texts but also a variety of multi-media information. The multi-media information includes not only text information but also various types of information, such as a still image, a moving image, an animation, a sound, and the like. Particularly, a moving image is the basis of a next-generation service, such as, a video on demand (VOD) service or an interactive service, so a study on a related draft standard is being actively made.
Due to a development of digital electronics engineering technology, conventional analog data is transformed into digital data. To effectively deal with a vast amount of digital data, a variety of techniques of processing a digital video material have appeared. Digital image processing techniques have the following advantages.
First, because noise is added to an original signal when each analog device performs a function, the quality of an image is degraded during a noise removal process. However, digital image processing apparatuses prevent the degradation of the image quality.
Second, since a signal is digitalized, the signal can be processed using a computer. Hence, signal processing, such as compression of image information or the like, is possible.
Digital image processing techniques relate to how analog data recorded on a medium can be represented using a computer. The possibility of a digital video was realized by a digital video interactive (DIV) system proposed by researchers at the RCA corporation at the end of the 1980's. The DIV system uses a special processor that is capable of microprogramming and executes a command suitable for image processing, thereby executing a function difficult to be processed in real time by general processors.
The Joint Photographics Experts Group (JPEG) and Motion Pictures Experts Group (MPEG), which were launched in 1989, set a standard coding method that is difficult to be implemented via hardware but has a performance exceedingly superior to that of the DIV system. Because the standard coding method is supported by many companies, it is anticipated to play an important role in the digital video development. In particular, MPEG standards have been continuously developed to, for example, MPEG II and then to MPEG III in order to achieve not only image processing on PCs but also digitalization of a high-definition system, such as, an HDTV.
Various techniques of processing an image using only the processing capability of a main processor without special hardware have been introduced since 1991. At present, representative examples of this technique include Apple's QuickTime, Microsoft's Video-for-Windows, and Intel's Indeo. Theses image-processing techniques are spotlighted especially by PCs because of a high-speed main processor.
This introduction of various digital image processing techniques causes a necessity for standardization. Due to the standardization, the digital image processing techniques are widely used, like being compatibly shared by not only a video conference system, a digital broadcasting codec system, and a video telephone industry but also a computer industry, a communications industry, and the like. For example, a digital video compression for information storage in optical disks, such as, CD-ROMs, or digital storage media is achieved by almost the same base technique as that used for compression for video communications and the like. Current MPEG standardization driven by ISO-IEC, JTC1, SC1, and WG11 is under progress since MPEG was launched in the 1990's.
However, a conventional video signal is processed in a three-dimensional color space of red (R), green (G), and blue (B) colors and displayed using three color light sources. The reason why a video signal is displayed using three color signals, namely, RGB signals, is that the three colors R, G, and B are primary colors which can be used to generate most remaining other colors. In general, in image display using three color light sources, namely, R, G, and B light sources, every color is represented by a combination of R, G, and B colors. In this case, representation of a composite color obtained using R, G, and B colors on a color coordinate is not enough. Since more colors can be recognized by a human being than colors obtained by combining three colors R, G, and B, colors that cannot be represented using R, G, and B can be represented by adding a new color to the three colors. Thus, a color close to a natural color can be represented.
FIG. 1 illustrates a relationship between primary colors used to represent a color. As illustrated in FIG. 1, every color signal can be represented by a combination of three primary colors, namely, R, G, and B. When R and G signals are combined, a yellow (Y) signal is produced. When G and B signals are combined, a cyan (C) signal is produced. When B and R signals are combined, a magenta (M) signal is produced. When the R, G, and B signals are all combined, a white (W) signal is produced.
FIG. 2 is a graph showing colors that can be recognized by human being and chromaticity coordinates of RGB-combined colors. As illustrated in FIG. 2, all of the chromaticity coordinates defined by a triangle of R, G, and B can be represented by combining three color signals, namely, R, G, and B color signals. However, it is not possible to reproduce colors existing outside the triangle of colors existing within a closed curve, which is an area of colors that can be recognized by human being, using only R, G, and B color signals.
FIG. 3 is a block diagram conceptually illustrating an operation of a conventional three-color display device. As illustrated in FIG. 3, the conventional three-color display device receives and displays an input signal having three color components Ri, Gi, and Bi.
The following techniques have been introduced as a method of converting an input signal into a color signal having multiple color components. First, U.S. Pat. No. 6,633,302 assigned to the Olympus Corporation discloses a color conversion performed using a XYZ color space. In systems using 5 or more primary colors, this color conversion includes a very complicate color-space division process and consequently its implementation is difficult.
Second, in a technique proposed by the Genoa Company, a three-dimensional lookup table is reduced to a two-dimensional lookup table, and the two-dimensional lookup table undergoes mapping. An additional one-dimensional lookup table is used to match sizes of two-dimensional color areas for luminance levels with one another. However, this technique also includes a very complicate lookup table calculating process. Furthermore, since a maximum chroma value and a maximum luminance value that can be represented by a multi-color display device vary depending on the type of a method used to convert a color space, the quality of an output image may be degraded.